1. Field of the Invention
The present invention generally relates to an improved driver for actuating a rotatable valve member. More specifically, the present invention is directed to a new, novel valve driver including a drive shaft and yoke having arms extending about and around the fluid path to loosely engage the rotatable member of a ball, plug or hemi-wedge valve.
2. Description of the Background
Ball valves, plug valves and the like are well known to those skilled in the art. The common characteristics of these valves is that they may be operated from fully open to fully closed by rotation through an angle of not more than about ninety degrees (90.degree.).
A simple plug valve comprises a rotatable, tapered plug having a bore therethrough disposed in a complementary housing. The plug valve permits fluid flow to be fully stopped by rotating the plug not more than about ninety degrees (90.degree.). However, these valves offer only minimal graduated control of fluid flow by setting the plug at intermediate positions and require modification for use in high pressure environments.
A ball valve comprises a rotatable ball having a bore therethrough corresponding to the fluid flow path, together with a seat for sealing with the ball surface. Ball valves operate similarly to the previously described plug valves and offer similar advantages and disadvantages.
Presently lesser known, but offering significant advantages over conventional ball and plug valves, is my hemi-wedge valve described in U.S. Pat. No. 4,962,911, which is hereby incorporated by reference. In short, the hemi-wedge valve includes a rotatable, curved wedge disposed in the fluid path together with a fixed thrust ball for displacing the wedge longitudinally toward the seat as the wedge is rotated between its open and closed positions. The hemi-wedge comprises a wedge having curved sides so that a first, convex side forms a curved sealing surface with the seat of the valve and a second, concave side forms a curved thrust surface for cooperation with a complementary curved, fixed surface on the thrust ball. Further, the thickness of the wedge increases from its leading end to its trailing end. The wedge includes a bore forming a part of the fluid path through its thinner, leading end and is solid at its thicker, trailing end. Rotation of the hemi-wedge through about ninety degrees (90.degree.) gradually closes the fluid path by blocking it with the thicker end of the wedge.
There are basically two systems used for turning the rotatable ball, plug or hemi-wedge of the foregoing valves. The rotatable valve member may be unconnected to or rigidly connected with the actuator. Each system satisfies a need, but neither accomplishes its goals without compromise.
In the first system used to actuate the rotatable member of a quarter-turn valve, the rotatable valve member is turned by an external actuator that is not connected to the ball, plug or hemi-wedge. This arrangement gives the rotatable member the chance to float within certain constraints so that the sealing surface of the rotatable member is able to seek a common sealing area with the valve seat. When this arrangement is employed, it is often necessary to provide pads or external bearing points to help prevent the rotatable member from being forced askew or cocked. If the rotatable valve member, e.g., a ball or plug, is forced askew, unwanted wear, scratching and impairment of the sealing surfaces often results. Cocking of the rotatable member also causes additional friction by rubbing the rotatable member against the inside surfaces of the valve housing, thereby increasing the operating torque required to actuate the valve.
The second system commonly used to actuate the rotatable member of a quarter-turn valve rigidly connects the actuator, and typically a diametrically disposed trunnion, to the rotatable member to prevent unwanted cocking. In this arrangement, a drive shaft and trunnion are rigidly connected to the rotatable member when disposed in a valve housing with a trunnion guide, thus forcing the rotatable member to rotate on the axis or true centerline of the actuating shaft. This configuration eliminates cocking and thus the need for pads or bearing surfaces to maintain the rotatable member centered. However, the rotatable member may no longer float when rigidly connected to the actuator and trunnion. Sealing becomes totally dependent upon pressure in the line or upon movement of the seat into sealing position with the rotatable member.
It is evident that neither of the foregoing described systems provides an ideal drive system. Where the rotatable valve member is permitted to float, it may be easily forced askew, resulting in increased wear to the sealing surfaces and requiring increased operating thrust. Where the rotatable valve member is rigidly connected to a drive shaft with or without a trunnion, the valve member will no longer be susceptible to such cocking. However, this benefit is achieved at the expense of seal integrity.
Accordingly, there has been a long-felt, but unfulfilled need for an improved drive mechanism for the rotatable member of quarter-turn valves, e.g., ball, plug and hemi-wedge valves. Those skilled in the art have long sought and will appreciate the novel and non-obvious features of the present invention and the improved valve resulting therefrom.